From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 66F01C3DA7A for ; Mon, 2 Jan 2023 11:27:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235914AbjABL1b (ORCPT ); Mon, 2 Jan 2023 06:27:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45646 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235993AbjABL06 (ORCPT ); Mon, 2 Jan 2023 06:26:58 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2AA863C2 for ; Mon, 2 Jan 2023 03:25:43 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3E5D160F49 for ; Mon, 2 Jan 2023 11:25:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55440C433EF; Mon, 2 Jan 2023 11:25:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1672658742; bh=qmgfQ9jAp7+N6zmG3v5IxLnG4vR6DuzquIepYQXwkRU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SOvIxIVP1vTNCLYxZDHPPTrHpcOlnoHmZFbiTIanYcPeJ4Z4IKlasrx0fbBtJnZqy 6EEO1Sv2n/rCiTfv/Uo02PqZrn8W2I562LPK8T8bOBypybsHFdJfwgHoIc6HP3Eyd3 64hKK0lveSo0qc09dTeDUn7Qo+Sln+1Pi8jCXAC0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Zhang Tianci , Jiachen Zhang , "Christian Brauner (Microsoft)" , Miklos Szeredi Subject: [PATCH 6.1 54/71] ovl: Use ovl mounters fsuid and fsgid in ovl_link() Date: Mon, 2 Jan 2023 12:22:19 +0100 Message-Id: <20230102110553.758530779@linuxfoundation.org> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230102110551.509937186@linuxfoundation.org> References: <20230102110551.509937186@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Zhang Tianci commit 5b0db51215e895a361bc63132caa7cca36a53d6a upstream. There is a wrong case of link() on overlay: $ mkdir /lower /fuse /merge $ mount -t fuse /fuse $ mkdir /fuse/upper /fuse/work $ mount -t overlay /merge -o lowerdir=/lower,upperdir=/fuse/upper,\ workdir=work $ touch /merge/file $ chown bin.bin /merge/file // the file's caller becomes "bin" $ ln /merge/file /merge/lnkfile Then we will get an error(EACCES) because fuse daemon checks the link()'s caller is "bin", it denied this request. In the changing history of ovl_link(), there are two key commits: The first is commit bb0d2b8ad296 ("ovl: fix sgid on directory") which overrides the cred's fsuid/fsgid using the new inode. The new inode's owner is initialized by inode_init_owner(), and inode->fsuid is assigned to the current user. So the override fsuid becomes the current user. We know link() is actually modifying the directory, so the caller must have the MAY_WRITE permission on the directory. The current caller may should have this permission. This is acceptable to use the caller's fsuid. The second is commit 51f7e52dc943 ("ovl: share inode for hard link") which removed the inode creation in ovl_link(). This commit move inode_init_owner() into ovl_create_object(), so the ovl_link() just give the old inode to ovl_create_or_link(). Then the override fsuid becomes the old inode's fsuid, neither the caller nor the overlay's mounter! So this is incorrect. Fix this bug by using ovl mounter's fsuid/fsgid to do underlying fs's link(). Link: https://lore.kernel.org/all/20220817102952.xnvesg3a7rbv576x@wittgenstein/T Link: https://lore.kernel.org/lkml/20220825130552.29587-1-zhangtianci.1997@bytedance.com/t Signed-off-by: Zhang Tianci Signed-off-by: Jiachen Zhang Reviewed-by: Christian Brauner (Microsoft) Fixes: 51f7e52dc943 ("ovl: share inode for hard link") Cc: # v4.8 Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman --- fs/overlayfs/dir.c | 46 ++++++++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 16 deletions(-) --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -592,28 +592,42 @@ static int ovl_create_or_link(struct den goto out_revert_creds; } - err = -ENOMEM; - override_cred = prepare_creds(); - if (override_cred) { + if (!attr->hardlink) { + err = -ENOMEM; + override_cred = prepare_creds(); + if (!override_cred) + goto out_revert_creds; + /* + * In the creation cases(create, mkdir, mknod, symlink), + * ovl should transfer current's fs{u,g}id to underlying + * fs. Because underlying fs want to initialize its new + * inode owner using current's fs{u,g}id. And in this + * case, the @inode is a new inode that is initialized + * in inode_init_owner() to current's fs{u,g}id. So use + * the inode's i_{u,g}id to override the cred's fs{u,g}id. + * + * But in the other hardlink case, ovl_link() does not + * create a new inode, so just use the ovl mounter's + * fs{u,g}id. + */ override_cred->fsuid = inode->i_uid; override_cred->fsgid = inode->i_gid; - if (!attr->hardlink) { - err = security_dentry_create_files_as(dentry, - attr->mode, &dentry->d_name, old_cred, - override_cred); - if (err) { - put_cred(override_cred); - goto out_revert_creds; - } + err = security_dentry_create_files_as(dentry, + attr->mode, &dentry->d_name, old_cred, + override_cred); + if (err) { + put_cred(override_cred); + goto out_revert_creds; } put_cred(override_creds(override_cred)); put_cred(override_cred); - - if (!ovl_dentry_is_whiteout(dentry)) - err = ovl_create_upper(dentry, inode, attr); - else - err = ovl_create_over_whiteout(dentry, inode, attr); } + + if (!ovl_dentry_is_whiteout(dentry)) + err = ovl_create_upper(dentry, inode, attr); + else + err = ovl_create_over_whiteout(dentry, inode, attr); + out_revert_creds: revert_creds(old_cred); return err;